The present invention relates to a method of manufacturing a solid-state image pick-up device, and more specifically to the method of manufacturing condenser lenses provided over light receiving portions of the solid-state image pick-up device.
In general, a solid-state image pick-up device is configured by arranging a plurality of solid-state image pick-up elements corresponding to pixels on a silicon substrate. The respective solid-state image pick-up element is composed of a light receiving portion (e.g. a photodiode) for transducing incident light into an electric signal and an electric charge transferring portion for transferring the transduced electric signal to a signal processing portion.
In order to decrease the size and increase the sensitivity of the solid-state image pick-up device as described above, it is well known such a method that condenser lenses are formed over the light receiving portions to condense the incident light onto the light receiving portions. This method is effective to improve the sensitivity of the received light, without increasing the size of the image pick-up device.
As a conventional method of manufacturing the condenser lenses, there have been known the method of RIE (reactive ion etching) technique, the method of deforming a thermally deformable resin patterned in accordance with the respective light receiving portions, etc.
FIG. 1 is a cross-sectional view showing the essential portions of the solid-state image pick-up device provided with the condenser lenses formed in accordance with the conventional method.
In the drawing, the device is formed by arranging, on a silicon substrate 301, light receiving portions 302 and electric charge transferring portions 303 having a gate electrode 303-1 and a light shading film 303-2, respectively. A transparent resin layer 304 is formed on these portions in order to make uniform the surface of the portions and further allow condenser lenses to become in-focus condition. Further, a plurality of semicylindrical condenser lenses 306 are formed on the transparent resin layer 304 so as to be located over the light receiving portions 302, respectively, with spaces (unavailable regions) 307 interposed between the two adjacent condenser lenses 306, respectively.
To form the above-mentioned condenser lenses 306, a thermally deformable resin layer such as photoresist, for instance is formed on the transparent resin layer 304; and the formed resin layer is further patterned to a thermally deformable striped resin layer so that each stripe of the resin layer is located over each light receiving portion 302. Further, the thermally deformable striped resin layer is heat treated to deform the layer into the shapes corresponding to the condenser lenses 306.
The above-mentioned unavailable regions 307 between the two adjacent condenser lenses 306 (which do not cover the solid-state image pick-up device) are necessary to prevent the two adjacent striped portions of the thermally deformable resin layer from being connected to each other during the heat treatment. In other words, the presence of the unavailable regions 307 serves to prevent both the ends of the condenser lenses from being formed irregularly in shape.
In the conventional method, therefore, since the areas of the unavailable regions 307 cannot be reduced so much, there exists a problem in that the light condensing efficiency of the condenser lens is inevitably reduced, with the result that it is impossible to further increase the light receiving sensitivity of the solid-state image pick-up device.
In addition, when the condenser lenses are formed in accordance with the conventional method, since the areas of the unavailable ranges 307 are not small, the quantity of light 308 allowed to be incident upon the unavailable regions 307 inevitably increases, as shown in FIG. 1.
Consequently, without only reducing the effective light signal components, the unavailable light are reflected at random from the surface or the inner portions of the transparent resin layer 304 and the light shading films 303-2, with the result that there raise other problems in that pairs of electron and hole are produced; smear is generated; and noise is increased, thus reducing the light receiving sensitivity of the solid-state image pick-up device.